This is a continuation of International Application PCT/EP00/08669, filed on Sep. 5, 2000, which was published in German under PCT Article 21(2), and which claimed priority to German application No. DE 200 05 123.7 (Mar. 20, 2000), the contents of both applications being incorporated herein by this reference.
Devices for testing circuit boards, especially non-componented circuit boards, may be characterized as either as finger testers and parallel testers.
Finger testers are devices in which the individual circuit board test points of a circuit board to be tested are probed in sequence by a probe arranged on a slide, which travels along a cross member over the circuit board to be tested. The probe is positioned over each circuit board test point to be probed, which is then contacted. One such finger tester comprises at least two contact fingers so that it can contact a track of the circuit board to be tested at two circuit board test points and test the section located in between. It can determine whether an open-circuit or short-circuit exists between the test points.
A finger tester is described, for example, in EP 0 486 153 A1. The described design permits the testing of a wide variety of circuit boards without requiring any mechanical modifications. In addition, all and any types of circuit boards can be tested with finger testers.
Parallel testers are testers that by means of a contact array, represented as a rule by an adapter, contact all or at least the majority of the contact locations of a circuit board to be tested simultaneously. Such parallel testers permit fast and safe scanning of a large number of circuit board test points.
The advantage of a parallel tester over a finger tester is that a parallel tester permits much faster testing of a circuit board since all measurements are implemented practically simultaneously. However, every time a change is made in the type of circuit board to be tested a new contact array needs to be provided which, as a rule, is done by producing a new adapter. Parallel testers are preferably put to use in high volume production since they permit a high testing throughput.
It thus follows directly from the above that one of the salient criteria for successful marketing of a finger tester is its speed in testing a circuit board since finger testers are inherently slower than parallel testers.
With the finger tester as known from EP 0 468 153 A1 both the front and rear sides of one or more circuit boards under test can be tested simultaneously. For this purpose two sets of contact fingers are provided, each of which is arranged on one of the two sides of a contact array. The contact array is, as a rule, oriented horizontal so that the one set of contact fingers is arranged above the contact array and the other below the contact array. The circuit boards to be tested are held in the tester, the finger tester, by means of two U-rails locating the circuit boards by their edges.
Also known is to use plate-type product holders for special circuit boards, which can be held by means of two rails opposite each other. Such special circuit boards typically have a shape that is not suitable for insertion in the rails or are floppy and need to be supported on all sides.
It is furthermore known in the case of finger testers to map by means of a camera the offset of each circuit board test point from its ideal position on a circuit board being tested and to take these offsets into account when positioning the contact fingers. Any misplacement of the circuit boards is likewise mapped and taken into account. The circuit boards to be tested are inserted against a stopper in the rails. The individual circuit board test points are then oriented in a system of coordinates defined by the stopper.
For parallel testers, it is known to compensate for any deviation in the actual position from the ideal position of the circuit board test points by shifting the circuit boards or the adapter accordingly. Such methods and devices are disclosed, for example, in U.S. Pat. No. 5,381,104, JP 4038480 and EP 0 874 243 A2. Also known are diverse devices that are used to align the circuit boards relative to the contact array, reference being made in this respect, for example, to EP 0 760 104 B1, U.S. Pat. Nos. 5,408,189, 4,820,975, EP 0 859 239 A3 and EP 0 831 332 A1. Apart from the optical methods of mapping deviations, methods of electrically sensing such deviations are known (e.g. EP 0 874 243 A2).
EP 0 722 090 A2 describes a holding fixture for flat test specimens, which supports the test specimen by retaining means on its two opposite surfaces. At least one of the retaining means is made of an electrically non-conductive film, which may be penetrated by contact fingers.
WO 00/17662 relates to a device for the testing of modules loaded with electrical components. It has a sample holder described as a tray, in which several modules loaded with electrical components may be inserted. These modules have electrical contacts in the area of one edge of their underside. In the area of this edge, the modules are contacted by a support element guidable from below and provided with contact deflection elements, by means of which the electrical contacts of the modules may be deflected upwards. A test head is lowered from above and contacts both these contact deflection elements and also the modules for is testing themselves.
xe2x80x9cOPEN-FRAME PRODUCT CRADLE FOR PROBINGxe2x80x9d IBM TECHNICAL DISCLOSURE BULLETIN, US, IBM CORP. NEW YORK, Vol. 38, No. 12, Dec. 1, 1995, pages 495-496 discloses a product holder in which multi-chip modules or circuit boards may be inserted. For each module and circuit board respectively an opening is provided, with fixing means for fixing the modules and/or circuit boards to the product holder.
The invention concerns a circuit board tester with enhanced throughput as compared to that of known devices. The invention is also intended to provide a suitable method for increasing the throughput of circuit boards during testing with a finger tester.
In general, according to one aspect, the invention features a circuit board tester in which arranged between the two sets of contact fingers is a holder comprising portions for accommodating at least two circuit boards to be tested. At least one of the circuit boards to be tested is insertable in the holder means with its front side, and the other circuit board to be tested with its rear side, facing one of the two sets of contact fingers. The controller is configured such that with both sets of contact fingers the circuit board test points on both the front and rear sides of the circuit board to be tested can be contacted during a test procedure.
The circuit board tester in accordance with the invention is configured such that the circuit boards can be arranged xe2x80x9creversiblexe2x80x9d, i.e. a certain number of circuit boards is arranged with their front side facing e.g. upwards and the other circuit boards with their rear side facing upwards. This exploits the property of the majority of popular circuit boards that one side features substantially more circuit board test points than the other. Indeed, a ratio of 10:1 is not unusual for the difference in the number of circuit board test points on the front side as compared to the rear side. That is, a circuit board to be tested may have on the front side 10,000 circuit board test points and only 1,000 circuit board test points on the rear side. Since in the device in accordance with the invention the circuit boards to be tested are arranged with both the front and rear sides facing a set of contact fingers and the controller is configured such that both the front and the rear sides of the circuit boards to be tested can be contacted by a set of circuit board test points, roughly the same number of circuit board test points is tested in each case by the two sets of contact fingers. When an even number of circuit boards can be inserted into the tester, preferably half of the circuit boards is arranged in the tester with the front side facing the one set and the other half of the circuit boards with the rear side facing the other set. This results in the same number of front sides and rear sides of both sets of circuit boards of the type under test being tested and thus both sets of contact fingers test the same number of circuit board test points. This arrangement ensures that both sets of contact fingers perform precisely the same amount of work per cycle.
In prior art testers only one of the two sets of contact fingers was utilized during a load/unload cycle, namely the set of contact fingers contacting the side of the circuit board to be tested having the most circuit board test points whereas the other set of contact fingers in prior art testers merely contacts a substantially smaller number of circuit board test points. This is the reason why during testing, this set of circuit board test points often has to wait idle until the other set of circuit board test points has concluded sensing. This dead time is eliminated or at least reduced to a minimum by the tester in accordance with the invention.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.